This invention relates to a flame retardant for synthetic resins, and particularly relates to a flame retardant for synthetic resins comprising an oligomer having repeated units of ##STR3## The flame retardant for synthetic resins of the present invention is stable to heat, does not substantially impair the properties of the synthetic resins and has flame retardance effect.
Generally, articles made from synthetic resin are flammable. A variety of flame retardants for synthetic resins, such as organic halides, and organic phosphorus compounds have been proposed in the prior art. However, some of the flame retardants of the prior art are unstable to heat. Some of the flame retardants which are stable to heat tend to discolor the articles made from synthetic resins incorporating the flame retardant and to lower the physical properties, such as the mechanical strength of said articles.
A variety of flame retardants have been developed in order to overcome the disadvantages of the flame retardants composed of the organic halide compounds. For example, in Japanese Public Disclosure No. 49- 131234 (laid open), a compound having the formula ##STR4## wherein X is O or S, m is integer of from 2 to 4 and l is integer of from 1 to 50 disclosed as a flame retardant for a synthetic resin. In Japanese Patent Publication No. 47- 44537, the compound having the formula ##STR5## wherein R is H or lower alkyl, m is integer of from 1 to 5 and n is integer of from 2 to 10 is disclosed as a flame retardant for a synthetic resin.
However, when these flame retardants are added to a polyester or polycarbonate which has flame retardancy property per se they enhance said flame retardance effect. However, when they are added to polystyrene, high-impact polystyrene or ABS resin which is flammable, they give little or no flame retardant property to the resin.
We have carried out experiments on flame retardancy of the compounds disclosed in Japanese Public Disclosure No. 49- 131234 (laid open). In high-impact polystyrene (sold under the trade name of "Styrone 492" by Asahi Dow Co.) were incorporated 20% by weight of such a compound and 5% by weight of antimony trioxide based on the total weight of high-impact polystyrene, the flame retardant and antimony trioxide. A molded article was formed from the resulting mixture. The flame retardancy of the article was tested in accordance with UL 94 test method (Standard for Flammability Tests of Plastic Materials for Parts in Devices and Appliance UL 94, Sept. 1973). The class of the retardancy was 94 v- 2. That is the drippings of the resin were observed to fall. This shows that the flame retardancy of the compound was not sufficient.
We have have also carried out an experiment on the flame retardancy of an oligomer of tetrabromobisphenol A polycarbonate disclosed in Japanese Public Disclosure No. 47- 44537. In polystyrene (sold under the trade name of "Styrone 666" by Asahi Dow Co.) were incorporated 20% by weight of said oligomer and 5% by weight of antimony trioxide based on the total weight of the polystyrene, flame retardant and antimony trioxide. A molded article was formed from the resulting mixture. The flame retardancy of the article was tested in accordance with Ul 94 Standard. The class of the flame retardancy was 94 v- 2. This shows that the flame retardancy of this compound, too, is not sufficient. In the above two experiments the class of UL 94 v- 2 in the test of UL 94 Standard shows that drippings of the resin fall on cotton cloth, thereby burning the cloth. This shows there is possibility of causing secondary ignition. Therefore, it was apparent from the above two experiments that the flame retardants as disclosed in Disclosure No. 49- 131234 and Publication No. 47- 44537 impart poor flame retardancy to high-impact polystyrene and polystyrene when incorporated therein. Consequently, there is need for a flame retardant for synthetic resins having such fire-retardancy effect that in case a resin containing the fire retardant burns, drippings of the resin do not fall.
Also, a tetrabromobisphenol A oligomer terminated with a halo-substituted phenol is disclosed in U.S. Pat. No. 3,846,469 as a flame retardant. However, it was found from our flaming-test that this oligomer had the same flame retardancy as that of an oligomer disclosed in Japanese Patent Publication No. 47- 44537.